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block: Allow omitting the file name when using driver-specific options

After this patch, using -drive with an empty file name continues to open
the file if driver-specific options are used. If no driver-specific
options are specified, the semantics stay as it was: It defines a drive
without an inserted medium.

In order to achieve this, bdrv_open() must be made safe to work with a
NULL filename parameter. The assumption that is made is that only block
drivers which implement bdrv_parse_filename() support using driver
specific options and could therefore work without a filename. These
drivers must make sure to cope with NULL in their implementation of
.bdrv_open() (this is only NBD for now). For all other drivers, the
block layer code will make sure to error out before calling into their
code - they can't possibly work without a filename.

Now an NBD connection can be opened like this:

  qemu-system-x86_64 -drive file.driver=nbd,file.port=1234,file.host=::1

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
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commit c2ad1b0c465a9ea8375eaff14bbd85705c673f73 1 parent f5866fa
Kevin Wolf authored
Showing with 51 additions and 11 deletions.
  1. +41 −8 block.c
  2. +7 −3 blockdev.c
  3. +3 −0  include/block/block_int.h
View
49 block.c
@@ -688,7 +688,11 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
bdrv_enable_copy_on_read(bs);
}
- pstrcpy(bs->filename, sizeof(bs->filename), filename);
+ if (filename != NULL) {
+ pstrcpy(bs->filename, sizeof(bs->filename), filename);
+ } else {
+ bs->filename[0] = '\0';
+ }
if (use_bdrv_whitelist && !bdrv_is_whitelisted(drv)) {
return -ENOTSUP;
@@ -708,6 +712,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
bdrv_swap(file, bs);
ret = 0;
} else {
+ assert(drv->bdrv_parse_filename || filename != NULL);
ret = drv->bdrv_file_open(bs, filename, options, open_flags);
}
} else {
@@ -727,6 +732,7 @@ static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
#ifndef _WIN32
if (bs->is_temporary) {
+ assert(filename != NULL);
unlink(filename);
}
#endif
@@ -753,14 +759,9 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
{
BlockDriverState *bs;
BlockDriver *drv;
+ const char *drvname;
int ret;
- drv = bdrv_find_protocol(filename);
- if (!drv) {
- QDECREF(options);
- return -ENOENT;
- }
-
/* NULL means an empty set of options */
if (options == NULL) {
options = qdict_new();
@@ -770,7 +771,26 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
bs->options = options;
options = qdict_clone_shallow(options);
- if (drv->bdrv_parse_filename) {
+ /* Find the right block driver */
+ drvname = qdict_get_try_str(options, "driver");
+ if (drvname) {
+ drv = bdrv_find_whitelisted_format(drvname);
+ qdict_del(options, "driver");
+ } else if (filename) {
+ drv = bdrv_find_protocol(filename);
+ } else {
+ qerror_report(ERROR_CLASS_GENERIC_ERROR,
+ "Must specify either driver or file");
+ drv = NULL;
+ }
+
+ if (!drv) {
+ ret = -ENOENT;
+ goto fail;
+ }
+
+ /* Parse the filename and open it */
+ if (drv->bdrv_parse_filename && filename) {
Error *local_err = NULL;
drv->bdrv_parse_filename(filename, options, &local_err);
if (error_is_set(&local_err)) {
@@ -779,6 +799,12 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename,
ret = -EINVAL;
goto fail;
}
+ } else if (!drv->bdrv_parse_filename && !filename) {
+ qerror_report(ERROR_CLASS_GENERIC_ERROR,
+ "The '%s' block driver requires a file name",
+ drv->format_name);
+ ret = -EINVAL;
+ goto fail;
}
ret = bdrv_open_common(bs, NULL, filename, options, flags, drv);
@@ -899,6 +925,13 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
QEMUOptionParameter *create_options;
char backing_filename[PATH_MAX];
+ if (qdict_size(options) != 0) {
+ error_report("Can't use snapshot=on with driver-specific options");
+ ret = -EINVAL;
+ goto fail;
+ }
+ assert(filename != NULL);
+
/* if snapshot, we create a temporary backing file and open it
instead of opening 'filename' directly */
View
10 blockdev.c
@@ -658,7 +658,11 @@ DriveInfo *drive_init(QemuOpts *all_opts, BlockInterfaceType block_default_type)
abort();
}
if (!file || !*file) {
- return dinfo;
+ if (qdict_size(bs_opts)) {
+ file = NULL;
+ } else {
+ return dinfo;
+ }
}
if (snapshot) {
/* always use cache=unsafe with snapshot */
@@ -697,10 +701,10 @@ DriveInfo *drive_init(QemuOpts *all_opts, BlockInterfaceType block_default_type)
if (ret < 0) {
if (ret == -EMEDIUMTYPE) {
error_report("could not open disk image %s: not in %s format",
- file, drv->format_name);
+ file ?: dinfo->id, drv->format_name);
} else {
error_report("could not open disk image %s: %s",
- file, strerror(-ret));
+ file ?: dinfo->id, strerror(-ret));
}
goto err;
}
View
3  include/block/block_int.h
@@ -75,6 +75,9 @@ struct BlockDriver {
int instance_size;
int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
int (*bdrv_probe_device)(const char *filename);
+
+ /* Any driver implementing this callback is expected to be able to handle
+ * NULL file names in its .bdrv_open() implementation */
void (*bdrv_parse_filename)(const char *filename, QDict *options, Error **errp);
/* For handling image reopen for split or non-split files */
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